High pressure valves, or chokes, are often positioned at the wellhead to control flow. There are three main types of chokes: manual chokes, which require the user to be physically in the manifold and operate the choke by hand as the gas flows through; hydraulic chokes, which allow the user to operate the choke remotely from the drilling floor or doghouse; and electric chokes, which also allow the user to operate the choke remotely and are able to perform consistently in varying environmental conditions as well as add digital capabilities to the choke.
At locations where oil or gas wells are being drilled, a number of flammable gases may be present, including mixtures of oxygen, methane, ethane, propane, hydrogen sulfide and others. Similar potentially dangerous environmental conditions exist in locations in which petroleum products are being recovered, refined or processed. Standardized classifications for various types of hazardous locations have been adopted and assigned by regulatory agencies according to the nature and type of hazard that is generally present or that may occasionally be present.
Because electrical components, by their nature, may generate heat and sparks sufficient to ignite a flammable gas or other flammable mixture under even normal operating conditions, such components must be carefully selected and installed when used in an area that is classified as hazardous. More specifically, the components must exceed certain minimum standards as to such characteristics as power consumption, operating temperature, current and voltage requirements, and energy storage capabilities. These standards are also established by regulatory authorities and vary depending upon the particular hazardous environment.
Chokes positioned at the wellhead are often located in areas that are classified as hazardous. As such, the use of electric chokes may be limited to uses where they are not at the wellhead or in a hazardous area. It would be an improvement to have an electric choke that could be used at the wellhead or in other hazardous areas.